Asthma, the most significant chronic lung disease in children, is strongly associated with sensitization to common indoor allergens. Our asthma program includes two studies: (a) a survey of allergen types and levels in the nation's housing to provide estimates of allergen exposure in the U.S. population (National Allergen Survey); and (b) a primary prevention trial to determine if environmental intervention aimed at reducing indoor allergen levels can prevent sensitization and decrease the prevalence of asthma in children at high risk for development of the disease (EIPPAC Study). The National Allergen Survey is a descriptive study of allergen types and levels in floor and bedding dust in the nation's housing. The survey design is a population-based, multi-stage area probability sample designed to represent all 50 states and the District of Columbia. It has approximately 850 homes in 75 primary sampling units. The major endpoints of the survey are measurements of allergen (Der f I, Der p I, Bla g I, Fel d I, Can f I, Mus m I, Rat n I, Alternaria) and endotoxin levels in dust collected from an array of sites in survey homes. The study will provide estimates of allergen exposure in the U.S. population and collect relevant data on housing conditions, demographic factors, and climate to facilitate evaluation of regional, ethnic, socioeconomic, and/or housing characteristic differences in the allergen burden. The EIPPAC Study is a clinical trial that will determine if environmental intervention aimed at reducing indoor allergen levels in homes can prevent sensitization and decrease the prevalence of asthma in high risk children. Pilot studies are being conducted to test the feasibility and effectiveness of various interventions to reduce indoor allergen levels in inner-city homes. Once an effective allergen reduction regimen is developed, approximately 500 children with a positive family history of asthma and/or allergy residing in low-income homes will be randomized, before birth, to one of two treatment groups: (a) comprehensive allergen reduction; or (b) placebo. Baseline data will include collection of dust from multiple household sites for measurement of allergens. All children and their dwellings will then be prospectively followed for six years with periodic clinical, immunological, and environmental assessments. This interventional study will provide important information concerning the role of environmental intervention in the primary prevention of asthma in children. This study will also provide insight into basic immunologic mechanisms operative during allergen sensitization and the expression of allergic diseases.